Regulation of skin blood flow (SkBF) in normal man represents the net effects of competing drives associated with exercise, upright posture, skin temperature and internal temperature. Efferent control of skin blood flow is manifest via sympathetic vasoconstriction and a separate sympathetic vasodilator mechanisms. Neurogenic control of sweat rate is postulated by some as a necessay intermediate step for active cutaneous vasodilation. The relationship of the various drives to the two arms of efferent control of SkBF is crrently unclear. The objectives of this proposal are to gain information relative to (a) whether the net SkBF response to completing drives involves simultaneous activation of both the vasoconstrictor and vasodilator systems, (b) whether sweat rate continues to parallel SkBF when there are competing drives, (c) whether the range of whole body skin temperature which yields reflex adjustments in skin is limited during rest but extended when vasoconstrictor outflow is augmented, (d) whether the reflex SkBF response to an increase in whole body skin temperature during exercise is a function of the internal temperature, (e) whether changes in cutaneous blood volume predictably accompany arterialor vasomotor adjustments to heat stress and exercise and (f) whether there is a graded response in SkBF to workload. Thus the overall objective is to gain a fuller understanding of how the sympathetic nervous system controls SkBF when thermoregulatory drives for vasodilation are in competition with nonthermoregulatory drives for vasoconstriction. This objective will be approached by controlling skin temperature, work load, or imposing other vasoconstrictor stimuli in patterns and combinations designed to uncover basic schemes of control, levels of priority, and consequences to the circulatory system. Such understanding will aid in the clinical management of patients with limited cardiac output by aiding in the clarification of the role of the skin circulation in such a setting.